Summary As the raw material base for forest products manufacturing shifts from old-growth to short-rotation plantation stock, the wood from these younger trees will contain larger proportions of juvenile wood. This in turn will influence the quality of forest products obtained. The pattern of specific gravity variation in these trees, which varies among the five most important Pacific Northwest species groups, is reviewed, and the nature of their differences is related to growth habit. The shade intolerance of some species is speculated to manifest itself in an early culmination of annual height inrement, after which specific gravity increases rapidly to a maximum. This is contrasted to shade-tolerant species, in which specific gravity may take several decades to attain a minimum value, followed by only moderate increases thereafter. In addition, faster growth rates in widely spaced plantation trees tend to depress specific gravity and advance the age at which these trees reach their minimum value, thereby compounding the overall wood density of deficit of short-rotation trees.Lower specific gravity, compounded with reduced lignin content in juvenile wood, negatively influences kraft pulp yield, but not pulp quality parameters such as sheet density, burst and tensile strength. Reduced wood density, coupled with larger fibril angles in juvenile wood, reduces average strength and stiffness of lumber from younger plantation trees. Mechanical stress rating needs to be adopted to segregate the strong, stiff material for engineered construction uses, because a large proportion of visually graded lumber from juvenile wood zones will not meet currently assigned stress values. Mechanical stress rating can ensure a continued stream of appropriate engineering grades from future tree supplies.

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The lengths of fibres from fast- and slow-grown black cottonwood trees were measured at comparable heights and ages. Fibre length was found to vary directly and significantly with both growth rate and age from pith. An additional investigation showed that fast-grown sprouts had longer fibres than slow-grown sprouts of equal age collected from the same stump source. The mechanisms regulating fibre length in trees are discussed briefly.

The scanty and conflicting literature on distribution and nature of crystals in the ray parenchyma of Abies is reviewed before results are presented from this study of 318 trees. Crystals of rhomboidal and elongated forms were regularly present, in descending order of frequency, in A. coticolor, A. grandis, A. magnifica, A . bracteata, and A. procera. Crystals were deposited predominantly in marginal ray parenchyma cells which died prematurely within a critical zone of sapwood. Both forms of crystals were regularly lacking in A . amabilis, A. balsamea, A. fiaseri, and A. Iasiocarpa, although fairly frequently elongated types were found in certain samples of the latter species. A pattern of very infrequent crystal distribution was found in association with juvenile wood in a single mature A. gratzdis, and in seedlings or saplings of several species.A quantitative scale of crystal frequency was developed and its application to wood species identification demonstrated. The lack of crystals in A. amabilis is offered along with other evidence to suggest a relationship between this species and those of the series Lasiocarpae Franco.Chemical characterization by thin-layer chromatography, atomic absorption, and histochemical procedures confirmed the older supposition that both forms of ray parenchyma crystals were calcium oxalate.

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